[P-PS06] Lunar Science and Exploration

[PPS06-13] Simulation of subsurface temperature change at the lunar polar regions

*Ryusuke Nishitani¹, Makiko Ohtake¹, Yusuke Nakauchi², Mitsuo Yamamoto², Hiroyuki Sato² (1.University of Aizu, 2.Japan Aerospace Exploration Agency)

Keywords:Lunar polar regions, Temperature

A lot of remote sensing data has been collected by lunar orbiters to confirm the existence of water ice on the Moon. Although no direct evidence of water has been found yet, the data suggesting water existence have been obtained. Lunar Exploration Neutron Detector instrument (LEND) onboard the Lunar Reconnaissance Orbiter has revealed the existence of hydrogen-concentrated regions in the lunar polar region (Mitrofanov et al., 2010). The hydrogen-concentrated regions were found not only in the permanently shadowed regions (PSRs) but also in the non-PSR, indicating that water ice may exist beneath the dry regolith in these regions. LEND can detect the existence of hydrogen in the top ∼1 m of the lunar surface (Mitrofanov et al., 2010). If all hydrogen is derived from water ice, it is estimated that there is ~0.5 wt% water below 1 m of the lunar surface (Sanin et al., 2017). To confirm whether water ice can exist stably beneath the lunar polar regions, it is necessary to estimate the temperature below the surface. Hayne et al. (2017) obtained subsurface temperature profiles for each location on the Moon using a one-dimensional thermal model. However, the solar flux used in the model is not adapted to the lunar polar region due to complex illumination conditions.
In this study, we investigated lunar subsurface temperature changes under various illumination conditions using a similar model as Hayne et al. (2017) with solar flux intensity and illumination duration as free parameters. The results revealed that the temperature at a depth of several cm is reached its maximum at night time because it takes time for heat from the solar flux to be transferred to the interior. The time it takes to reach the maximum temperature depends on the solar flux intensity and the illumination duration. As the solar flux intensity is weaker and the illumination duration is shorter, the time to reach maximum temperature is longer. By comparing the results of thermal simulations with the simulated illumination condition at the south polar regions, the subsurface temperature change at the south polar regions was estimated.